Electroplating process



United States Patent ELECTROPLATIN G PROCESS Alfred Kirstahler,Dusseldorf, and Wennemar Strauss and Wolf-Dieter Willmund,Dusseldorf-Holthausen, Germany, assignors to'Dehydag, DeutscheHydrierwerke G. 111. b. IL, Dusseldorf, Germany, a corporation ofGermany No Drawing. Application October 25, 1956 Serial No. 618,183

Claims priority, application Germany June 15, 1956 Claims. (Cl. 204--44)wherein R is a straight-chain or cyclic organic radical comprising atleast two carbon atoms linked exclusively to oxygen, sulfur and/ornitrogen atoms, each of said carbon atoms being linked to a S-R SO Hgroup,

R is a bivalent lower aliphatic radical, and n is an integer equal tothe number of said carbon atoms in the radical R, or water-soluble saltsof such compounds.

For example, triazine derivatives having the structural formula Lia-Seanwherein R, has the meaning above indicated, or their water-solublesalts, such as the alkali metal or ammonium salts, are suitable asbrightening additives for electroplating baths in accordance with thepresent invention. The bivalent radical R may, for instance, be amethylene, ethylene, propylene, hydroxypropylene, chloropropylene orsimilarradical.

Such triazine compounds may, for example, be obtained by transformingtricyanogen chloride into trimercaptocyanuric acid, and thereafterreacting an alkali metal salt of the acid with an organichalogensulfonic acid, such as 2bromoethane-1'-sulfonic acid,3-bromopropane-l-sulfonic acid, 3-chloro 2 hydroxypropane-l-sulfonicacid or their alkali metal salts, or with a sultonc, such aspropanesultone or butanesult'one, to form the correspondingmercapto-alkanesulfonic acid triazine derivatives or their salts.

Other suitable compounds havingthe above general Formula I are thosewherein the radical R is a 5- or 6- membered heterocyclic radical withat least two nitrogen atoms. Compounds of this type are, for example,1,3,4- thiodiazole-2,5-bis(mercaptopropane-l-sulfonic acid) PatentedAug. 26, 1958 ice , 2 1,3,4-thiodiazole-2,5-bis(mercapto 2hydroxypropanel-sulfonic acid) or 1,3,4 oxdiazole 2,5bis(mercaptopropane-Lsulfoiric acid) and the like, or theirwater-soluble salts, such as alkali metal and ammonium salts.

As previously pointed out, however, the radical R in Formula I need notnecessarily be a cyclic radical. Thus, similarly suitable for use asbrightening agents in electroplating baths in accordance with thepresent invention are acyclic compounds, such asdithiobiuret-S,S'-dipropanesulfonic acid wherein R, has the meaningdefined in Formula I and R is an aliphatic of aromatic radical, andtheir watersoluble salts. The dibas'ic S-alkanesulfonic acids may beobtained, for example, by reacting methylene, ethylene, hexamethyleneorphenylene-dithiourea with propanesultone, butanesultone orhalogen-alkanesulfonic acids or alkali metal salts thereof,

Finally, also tribasic and higher polybasic S- alkanesulfonic acids andtheir water-soluble salts, such as those obtained by reacting polyureacompounds with halogenalkanesulfonic acids or sultones in accordancewith the above method, are effective as brightening agent's according tothe present invention.

The b'righteners disclosed herein may advantageously be employed inconjunction with all types of electroplating baths, and especially withelectroplating solutions for the production of copper, nickel, silver,zinc, cadmium, bronze and brass electrodep'osits.

While the brightening additives in accordance with the present inventionwill produce bright and lustrous metal electrodeposits when used as thesole additives in electroplating baths, they may also be employed incombination with known brightening additives, smoothing agents,sequestering agents, inhibitors, anionic, cationic or electroneut'ralsurface-active agents, salts which increase the conductivity of the bathand similar additives customarily used to improve the metalelectrodeposits.

For example, suitable additional brightcners are those which aredisclosed in copending application Serial No. 442,199, filed July 8,1954. Examples of sequestering agents are compounds disclosed incopending applications Serial No. 458,984, filed September 28, 1954, andSerial No. 544,586, filed November 2, 1955, and in German Patent No.934,508; in other words, the term sequestering agents is intended todesignate those additives which prevent the mineral salts in hard waterand impurities in the inorganic metal salt from interfering with thebrightening effect of the brightening additive.

The quantity of the S-alkanesulfonic acid compounds added toelectroplating baths according to the present invention may range from0.01 to 20 gm. per liter of bath. The effective current density range ofsuch electroplating baths lies between 0.5 and 12 amp./dm. and thetemperature of the solution may reach as high as 60 C.

during the electroplating procedure. The current density range at whichthe optimum brightening effect is achieved will vary from one particularbrightener to the other, but in general the range is of considerablebreadth for the entire group of brighteners herein disclosed. Theoptimum current density range may, however, be broadened by employing amixture of two or more members of the group.

Particularly noteworthy is the fact that the addition of theS-alkanesulfonic acid compounds described herein to electroplating bathsmakes it possible to produce fullbright electroplates within anexceptionally broad range of temperatures, namely between 15 and 60 C.At temperatures higher than room temperature the optimum current densityrange is shifted toward considerably higher values (about 15 amp./dm.Moreover, because of the ability of our brightening agents to producefullbright electrodeposits at relatively high bath temperatures, it ispossible to use the brighteners in copper-plating baths which because ofhigh rates of current flow develop a considerable amount of heat andtherefore operate at temperatures up to 40 C. and even 50' C.

Electroplating baths modified in accordance with our invention may beemployed to deposit metal electrodeposits on any desired customary basemetal, such as iron, steel, zinc and similar non-precious metals oralloys thereof. In the case of copper-plating baths, the base metal mayfirst be provided with a thin copper coating in a separate cyanide bathin customary fashion, or the base metal may be provided directly withthe final copper plate without a preliminary thin copper base coat inaccordance with the process disclosed in copending application SerialNo. 458,983, filed September 28, 1954.

In all cases, electroplating baths modified in accordance with thepresent invention produce full-bright electrodeposits of extraordinaryhigh quality which do not require subsequent bufling or polishing.

The following examples will further illustrate the present invention andenable others skilled in the art to understand it more completely. Itwill be understood, however, that the invention is not limited'to theseparticular examples.

Example I were dissolved in an acid aqueous copper sulfate bath-composed of water, 220 gm. per liter crystalline copper sulfate and 60gm. per liter sulfuric acid. Sheet metal objects copper-plated in thiselectroplating solution at room temperature and at elevated temperaturesup to 60 C. with a current density from 0.5 to 8 amp./dm.

were provided with a full-bright copper clectrodeposit which did notrequire bufling or polishing.

I Example II The same full-bright copper electrodeposits were obtainedwhen 0.2 to- 1.5 gm. per liter of the trisodium salt -(CHzh-BOaNB.

were added to the acid copper sulfate solution described in Example Iinstead of the trisodium salt of1,3,5-triazine-2,4,6-tri-(mercaptopropane 1 sulfonic acid), and brassand iron objects were copper-plated therein under the conditions oftemperature and current density described in Example I.

Example III 0.5 to 1.0 gm. per liter of the disodium salt of 1,8,4-thiodiazole-Z,S-bis-(mercaptopropane 1 sulfonic acid) having thestructural formula was added to an acid copper sulfate solution composedof water, 200 gm. per liter crystalline copper sulfate and 60 gm. perliter sulfuric acid. Brass and iron objects electroplated in thissolution at current densities from 2 to 10 amp./dm. and at temperaturesbetween room temperature and C. were provided with a full-bright,high-quality copper plate which required no buifing or polishingsubsequent to rinsing.

Example IV 0.2 to 1.0 gm. per liter of the dipotassium salt ofN,N-methylene-di-(isothiourea-S-propane 1 sulfonic acid) having thestructural formula was added to the acid copper sulfate solution ofExample III instead of the disodium salt of l,3,4-thiodiazole-2,5-

bis-(mercaptopropane-l-sulfonic acid). Brass and iron objectselectroplated in this modified copper sulfate bath at current densitiesfrom 1 to 11 amp./dm. and at temperatures between room temperature andabout C. were provided with full-bright, high-quality copper plateswhich required no bufiing or polishing.

Example V 1.2 gm. per liter of the trisodium salt of 1,3,5-triazine-2,4,6-tri-(mercaptopropane-Z-hydroxy 1 sulfonic acid) having thestructural formula shown in Example II and 0.8 to 1.2 gm. per liter1,3-bis-(dibutylamino)-propanol-2, described in said copendingapplication Serial No. 458,984,

were added to an acid copper sulfate solution composed of water, 220 gm.per liter crystalline copper sulfate and gm. per liter sulfuric acid.Brass and iron objects electroplated in this solution at temperaturesfrom room temperature to 60 C. and at current densities from slightlyabove 0 amp./dm. up to 15 amp./dm. were provided with full-bright copperelectrodeposits of exceptionally high quality which required noadditional bufl'ing or polishing. i

Example VI From 1 to gm. per liter of the ammonium salt of1,3,5-triazine-2,4,6-tri-(mercaptopropane 2 hydroxy-lsulfonic acid)having the structural formula Example VII From 0.5 to 1.5 gm. per literof the disodium salt of 1,3,4 thiodiazole-2,5-di-(mercaptopropane 1sulfonic acid) having the structural formula were dissolved in a zinccyanide bath composed of water, 57 gm. per liter zinc cyanide, 72 gm.per liter sodium hydroxide and 40 gm. per liter sodium cyanide. Sheetsteel electroplated in this solution at current densities from 1 toamp./dm. and at temperatures between room temperature and about 40 C.were provided with full-brigl1t zinc electrodeposits of extremely highquality which re quired no additional bufling or polishing.

Example VIII From 1 to 2 gm. per liter of the disodium salt of N,N-methylene-di-(isothiourea S-propane 1 sulfonic acid) having thestructural formula were dissolved in a cadmium cyanide bath composed ofwater, 125 gm. per liter cadmium sulfate, 140 gm. per liter sodiumcyanide and 72 gm. per liter sodium hydroxide. Steel and iron objectselectroplated in this solution at current densities from 3 to 8 amp./dm.and at temperatures between room temperature and about 35 C. wereprovided with full-bright cadmium electroplates of extremely highquality which required no further bufiing or polishing.

Example IX 1.0 gm. per liter of the trisodium salt of 1,3,5-triazine-2,4,6-tri-(mercaptopropane 1 sulfonic acid) having the structuralformula shown in Example II, 0.05 gm. per literN,N-diethyl-dithiocarbamic acid-ethylester-w-sodium sulfonate and 1.2gm. per liter 1,3-bis-(diethylamino)- propanol-2, as well as 0.5 gm. perliter of the sodium salt of an acid sulfuric acid ester mixture ofethoxylated fatty alcohols with alkyl radicals having from 12 to 18carbon atoms, were dissolved in an acid copper sulfate bath composed ofwater, 220 gm. per liter crystalline copper sulfate and 60 gm. per litersulfuric acid. Iron objects electroplated in this solution at 40 C. andat a current density "between 5 and 12 amp./dm. were provided with fullbright copper electroplates of extremely high quality, even when theiron objects had not previously been provided with a preliminary copperplate in a copper cyanide solution.

Example X The disodium salt of the1,3,4-thiazole-2,5-bis-mercapto-2'-oxypropane-1'-sulfonic acid wassubstituted for 6 the thiadiazole derivative in Example HI. Afullabright copper plate was obtained.

Example XI The disodium salt of the1,3,4-triazole-2,5-bis-mercaptopropane-1-sulfonic acid was used insteadof the triazin derivatives according to Example II. An excellent copperplate was obtained.

Example XII The dipotassium salt ofN,N'-m'ethylene-di-(isothiourea-S-prop-ane-l-sulfonic acid) according toExamples IV and VIII is substituted by an equal amount of the salts ofthe corresponding ethylene, hexamethylene or phenylene derivatives.Full-bright copper electroplates were obtained.

Example XIV The disodium salt of the dithiobiuret-S,S'-dipropanesulfonic acid was substituted for the N,N'-methylene-di-(isothiourea-S-propane-l-sulfonic acid) in Example VIII. A good brightcopper plate was formed.

While we have disclosed various specific embodiments of our invention,it will be apparent to persons skilled in the art that the presentinvention is not limited to these specific embodiments and that variouschanges and modifications may be made without departing from the spiritof the invention or the scope of the appended claims.

We claim:

1. An electroplating bath for producing bright electrodeposits of metalsselected from the group consisting of copper, zinc, cadmium, nickel,silver, bronze and brass, comprising an aqueous solution of an inorganicsalt of the metal to be electrodeposited and, as a brightener, anorganic sulfonic acid compound having the general formula wherein R isselected from the group consisting of straightchain and cyclic organicradicals comprising at least two carbon atoms linked exclusively toatoms selected from the group consisting of oxygen, nitrogen and sulfur,each of said carbon atoms being linked to an SR --SO X group, R is abivalent lower aliphatic radical, X is selected from the groupconsisting of hydrogen, alkali metal and ammonium, and n is an integerequal to the number of said carbon atoms in the radical R, saidbrightening agent being present in suflicient amount to effect thebrightening action.

2. An electroplating bath according to claim 1, wherein R is a1,3,5-triazine radical.

3. An electroplating bath according to claim 1, wherein R is a1,3,4-thiodiazole radical.

4. An electroplating bath according to claim 1, wherein R is aN,N-methylene-di-isothiourea radical.

5. The process of producing bright and lustrous deposits of metalselected from the group consisting of copper, zinc, cadmium, nickel,silver, bronze and brass, which comprises electrodepositing said metalfrom a bath containing said metal in the form of an aqueous solution ofan inorganic salt of the metal in the presence of a brightening agenthaving the general formula wherein R is selected from the groupconsisting of straight chain and cyclic organic radicals comprising atleast two carbon atoms linked exclusively to atoms selected from thegroup consisting of oxygen, nitrogen and sulfur, each of said carbonatoms being linked to an SR SO X group, R is a bivalent lower aliphaticradical, X is selected from the group consisting of hydro- 7 gen, alkalimetal and ammonium, and n is an integer equal 9. The electroplating bathv.of claim 1 wherein the to the number of said carbon atoms in theradical R, said quantity of brightener in said bath is between about0.01 brightening agent being present in sufficient amount to to20gin/liter. efiect the brightening action. 10. The process of claim 5wherein the quantity of 6. The process according to claim 5, wherein Ris a 5 brightener used is between about 0.01 to 20 gm./liter.1,3,5-triazine radical.

7. The process according to claim 5, wherein R is a s mn Cited in thefile of this Patent 1, h 1 radical- UNITED STATES PATENTS 8. The processaccording to claim 5, wherein R is a N,N-methylene-di-isothiourearadical. 10 2647866 Brown 1953 UNITED STATES PATENT OFFICE U CERTIFICATEOF CORRECTION Patent No 2,849,352 August 26, 1958 Alfred Kirstahler etal,

of the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 2, lines 3 to 5 for that portion of the formula reading OH OHExample I, for that portion of the formula reading "NaO S=" read NaO S==column '4, 'linevl4, Example II, for that portion of the formula'reading"NaO SN" read Na0 s= n,

Signed and sealed this 30th day of December 1958., Attest:

KARL AXLINE ROBERT C. WATSON Attcsting Officer Commissioner of Patents

1. AN ELECTROPLATING BATH FOR PRODUCING BRIGHT ELECTRODEPOSITS OF METALSSELECTED FROM THE GROUP CONSISTING OF COPPER, ZINC, CADMIUM, NICKEL,SILVER, BRONZE AND BRASS, COMPRISING AN AQUEOUS SOLUTION OF AN INORGANICSALT OF THE METAL TO BE ELECTRODEPOSITED AND, AS A BRIGHTENER, ANORGANIC SULFONIC ACID COMPOUND HAVING THE GENERAL FORMULA